<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="../../vue.js"></script>
</head>

<body>
  <div id="app">
    <button @click="isHot=!isHot">修改天气</button>
    <h1>今天天气真{{isHot?"热":"冷"}}</h1>
    <img :src="url" alt="">
  </div>
  <script>
    Vue.config.productionTip = false
    const vm = new Vue({
      el: "#app",
      data() {
        return {
          isHot: true,
          url: "./re.webp"
        }
      },
      //watch配置项
      watch: {
        //监听isHot属性
        isHot: {
          //当isHot发生改变的时候,handler函数就会执行
          //两个参数,第一个参数是新的值,第二个参数是原来的值
          handler(newValue, oldValue) {
            // console.log(a,b,c);

            //根据当前的值 去修改url的地址
            // newValue?this.url = "./re.webp" : this.url = "./leng.gif"

            this.url = newValue ? "./re.webp" : "./leng.gif"
          }
        }
      }
    });
  </script>
</body>

</html>